A second storey extension in Canberra costs $4,800 to $7,500+ per square metre with Rentoule Projects in 2026, and most full upper-floor additions we price (two or three bedrooms, a bathroom and new stairs) sit between $300,000 and $700,000. A fully compliant second storey on a single house can go ahead without a development application, but many Canberra projects need one because the new upper floor pushes outside the building envelope or the solar envelope protecting a neighbour's northern boundary.
I'm Jeff Rentoule. I've been in the building industry for 19 years and running Rentoule Projects for the last five. Going up is one of the most common questions I get from families who love their suburb but have run out of room, particularly on smaller blocks where a ground floor extension would eat the backyard. It's also the extension type with the most ways to go wrong if the structure, the planning rules and the budget aren't checked before anyone starts drawing. This guide covers what it costs, whether your house can take it, the ACT rules that decide your approval pathway, and when going up stops making sense.
What a second storey extension costs in Canberra
Second storey work costs more per square metre than a ground floor extension. Ground floor extensions with us run $3,200 to $5,200 per square metre. Going up starts at $4,800 and runs past $7,500 for complex structural work and premium finishes. The gap comes from work you don't see in the finished rooms: checking and strengthening what's underneath, taking the roof off, protecting the house from weather while it's open, scaffolding, and fitting a staircase into a floor plan that was never designed for one.
| Upper floor size | What it usually holds | Indicative build cost (inc GST) |
|---|---|---|
| Around 40m² | Main bedroom, ensuite and walk-in robe, or a retreat | $190,000 to $300,000 |
| Around 60m² | Two bedrooms and a bathroom | $290,000 to $450,000 |
| Around 80m² | Three bedrooms, a bathroom and a study or rumpus | $380,000 to $600,000+ |
Those ranges cover the build. Design, engineering, surveying, energy assessment and certifier fees sit on top and are paid direct to each consultant. A recent upstairs extension we priced, with a new rumpus and a deck, came in at about $365,000. Most projects also pick up downstairs work once the stairs go in, which is why the full range in our Canberra Renovation Guide runs from $300,000 to $700,000+.
The items that move a second storey price the most:
- Footings and lower walls. If the engineer says the existing footings or walls can't carry the new load, you're paying for new posts, beams or underpinning before a single upstairs room is built.
- Stair position. A staircase takes space from the ground floor. Putting it where it works upstairs and downstairs often means reworking a hallway, a bedroom or the living area.
- Roof form. A simple gable or skillion over the new floor is cheaper than matching a complex hip roof or building a feature roofline.
- Wet areas upstairs. A bathroom or ensuite on the upper floor needs plumbing routed down through the house, which is quite often the most awkward part of the services.
- Asbestos. Homes built before the mid-1980s often have it in eaves, wall sheeting or under floor coverings. Testing and licensed removal need to be allowed for before the roof comes off.
Can your house take a second storey?
This is the first question to answer, and the answer comes from an engineer. Before any concept plans, I get a structural engineer to look at what's there. They check the footings, the slab or subfloor, the load paths through the walls, and the soil. A lot of Canberra sits on reactive clay, so footings that have been fine under a single-storey house for 50 years may not be fine under two.
The 1960s and 1970s brick veneer homes common across Kambah, Wanniassa, Weston Creek and the older parts of Belconnen fall into three broad groups:
- The structure can carry it with minor strengthening. The simplest case, and the one where a second storey offers the best value.
- The structure needs independent support. The upper floor is carried on new posts and beams running down to new footings, so the old walls don't take the load. This works well but adds cost and affects the ground floor layout.
- The structure isn't worth building on. If the footings need major work and the ground floor needs a full renovation anyway, the numbers start pointing towards a knockdown rebuild instead.
Building over an existing garage is sometimes a cheaper way to get the same space, because the garage structure is easier to replace or reinforce without disturbing the living areas. It's worth asking about early if your garage sits on a side of the block where an upper floor won't overshadow the neighbours.
Do you need a DA for a second storey in the ACT?
Not always. Under the ACT Government's single dwelling rules, building or altering a single dwelling generally doesn't need development approval if it stays the only dwelling on the block, complies with the relevant development controls, meets the general exemption criteria, and the neighbours have been given information about the proposal.
For a second storey, the controls that decide it are in the Single Dwelling Housing Development Control. For an RZ1 block the main ones are:
- Storeys and height. A maximum of two storeys, and a maximum building height of 8.5 metres above datum ground level.
- Building envelope. On mid sized and large blocks, the house has to sit inside planes projected at 45 degrees from 3.5 metres above each side and rear boundary.
- Solar building envelope. The house has to sit inside planes projected at 31 degrees from a "solar fence" on the northern boundary of any adjoining residential block. On large blocks the solar fence is 2.4 metres in the primary building zone and 1.8 metres elsewhere. On mid sized and compact blocks it is 3 metres and 2.3 metres.
- Upper floor setbacks. On large blocks an upper floor wall needs at least 3 metres to the side boundary in the primary building zone, 6 metres to the side boundary in the rear zone, and 6 metres to the rear boundary. Unscreened elements such as balconies need 6 metres.
The solar envelope is where most second storeys run into trouble. If your neighbour sits to the south of you, your new upper floor can easily cast more shadow over their block than the envelope allows. That's why the shadow diagrams matter so much at concept stage.
If the design breaks one of these controls only slightly, you can apply for an exemption declaration instead of a full DA. It covers minor encroachments into setbacks, the building envelope, the solar envelope and private open space dimensions. The guidance says a height departure of more than 1000mm from the building envelope, or more than 700mm from the solar envelope, is generally not minor. Heritage-listed blocks generally can't use this route.
Anything beyond that needs a DA. Whichever pathway applies, you'll still need building approval from a certifier before work starts, and the DA or exemption declaration has to be in place first. Our guide to DA approval in the ACT covers the process in more detail.
Going up or going out
On a large Canberra block with a decent backyard, a ground floor extension is almost always cheaper per square metre and less disruptive. Going up makes more sense when:
- Site coverage is close to the limit. On large blocks the maximum is 40 per cent of the block area, and private open space has to stay at least 60 per cent of the block, less 50 square metres. A ground floor extension can hit those limits quickly.
- You want to keep the backyard. Families with young kids or a big established garden often prefer to give up nothing at ground level.
- The block has a view or better light up high. Common on sloping blocks in suburbs such as Red Hill, Hughes and Farrer.
- The ground floor already works. If the kitchen and living areas are fine and you only need bedrooms, putting them upstairs avoids pulling apart a good ground floor.
Our home extension cost guide compares ground floor, wraparound and second storey pricing side by side.
Timeline and living through it
Allow 4 to 8 weeks for design, then the approval pathway. An exempt project moves straight to building approval once neighbour information has been provided. An exemption declaration or DA adds assessment time on top. On site, a second storey addition usually takes 20 to 28 weeks.
Most families move out for at least part of the build. Once the roof comes off, the house is open to the weather, dust is constant and services get disconnected at times. Some projects are staged so you can stay for the early and late phases, but plan your budget on the assumption you'll need somewhere else to live for a few months. If you're still weighing up whether to go up, rebuild or move, our renovate, extend, rebuild or move guide walks through how I'd make that call.
Frequently asked questions
How much does a second storey extension cost in Canberra?
With Rentoule Projects in 2026, second storey additions cost $4,800 to $7,500+ per square metre. A 40 square metre upper floor typically sits at $190,000 to $300,000, and a full two or three bedroom upper floor with a bathroom and stairs usually runs $300,000 to $700,000. Design, engineering and certifier fees are extra.
Can I add a second storey without a DA in the ACT?
Yes, if the house stays a single dwelling and the design complies with the Single Dwelling Housing Development Control, including the two storey limit, 8.5 metre height limit, building envelope, solar envelope and setbacks. You must also give neighbours written information. Minor departures may suit an exemption declaration. Larger departures need a DA.
How do I know if my house can support a second storey?
Get a structural engineer to inspect it before you pay for design. They check the footings, slab or subfloor, wall load paths and soil. Many Canberra homes can carry an upper floor with strengthening. Others need a new independent structure of posts and beams, which adds cost but avoids loading the old walls.
Is a second storey cheaper than a knockdown rebuild?
Usually, if the existing house is structurally sound and the ground floor mostly works. A knockdown rebuild with us runs $3,500 to $5,500+ per square metre across the whole home, plus demolition. If the footings need major work and the ground floor needs a full renovation too, a rebuild can be the better value.
How long does a second storey extension take?
Allow 4 to 8 weeks for design, then the approval pathway, which is shortest for exempt projects and longer for a DA. Construction on site usually takes 20 to 28 weeks. Most families move out for at least part of that time because the roof is removed and the house is open to the weather.
Start with the structure and the shadows
The two things that decide a second storey are whether the house can carry it and whether the shadow it casts stays inside the solar envelope. Get those answered first and the design, approval pathway and budget all follow from there. I'd rather tell you early that your house isn't a good candidate than have you spend money on drawings for something that won't stack up.
If you're thinking about going up in Canberra, get in touch. Coffee's on me.